For a more accurate depth of field photography, the user of the camera normally relies on the depth of field scale. The operation involves the following six steps, one after the other: (a) Focusing one boundary point of the desired depth of field range. (b) Reading and memorizing the selected distance. (c) Focusing the other boundary point. (d) Reading and memorizing this second selected distance. (e) Rotating the focusing ring until the two memorized distances face the same stop numbers of the depth of field scale. (f) Adjusting the diaphragm in accordance with these stop numbers.
My Swiss Pat. No. 517,314 discloses a camera embodying a device which automatically performs the aforediscussed series of manipulations. No satisfactory construction of an objective which can carry out such manipulations is known as yet. However, the automatic exposure time device which is disclosed on page 3, lines 6 and 7 of the Swiss Patent has been incorporated in the meantime in at least 16 modern cameras. Moreover, there are many additional proposals relating to automated focusing aids. When photographing, only the selection of depth of field would still require manual adjustment including the four steps b, d, e and f during which the camera is not trained upon the subject or scene. Therefore, there exists a need for an objective which is capable of carrying out these manipulations in an automatic way.